Oceanic near-surface current variability induced by interior dynamics: experimental and numerical simulations

Abstract

Surface vorticity in the oceans is usually driven by wind dynamics. However, in semi-enclosed and stratified basins - like the Mediterranean - internal ocean processes may dominate the development of surface as well as interior vorticity. A possible scenario for this particular case is the Ionian Sea, the deepest sea of the Mediterranean, in which near-surface circulation periodic (decadal) reversals appear not to be entirely explained by atmosphere-ocean interactions, suggesting the predominance of interior dynamics over the wind forcing. The theory of the Adriatic-Ionian Bimodal Oscillating System (BiOS) proposes that the redistribution of water masses, related to variations in the thermohaline properties of the Southern Adriatic, is the main driver of those vorticity inversions. In order to access such phenomena, a set of experiments was performed at the Legi Coriolis Rotating Platform, a rotating tank with 13m diameter that allows reproducing ocean behavior under the influence of Earth rotation. The topography and water inlets of the Ionian Sea were reproduced in the tank and velocity fields were analyzed using, among other techniques, Particle Image Velocimetry (PIV). In this thesis, the experiments performed at the rotating tank were documented, analyzed and simulated using a multi-layer numerical model. Case studies, comparing PIV measurements and model results were considered. Moreover, the model was improved to consider turbulent entrainment between the layers.